A data processor typically executes program instructions sequentially. Often, however, either internal requests from within the data processor or external requests from devices peripheral to the data processor necessitate the execution of interrupt service routines. Interrupt service routines are sets of instructions which enable the data processor to respond appropriately to these internal or external requests. To allow for execution of the interrupt service routine, the interrupt request signals are asserted and normal operation of the data processor is temporarily suspended. Commonly, the interrupt request signal may be identified by an assigned priority level. Therefore, if several interrupt request signals are asserted simultaneously, the signal with the highest priority will be serviced first. This type of prioritization system generally results in a more efficient data processor which is able to quickly service interrupt requests which are vital for operation before processing those interrupt requests which are not as significant. However, the time necessary to service each of the interrupt request signals increases in such a system since the priority levels of each of the interrupt requests must be compared to determine the highest priority. Current technology permits the priority of the interrupt request signals to be determined by hardware implementations, software programs or a system involving both. In many cases, the established priority of an interrupt request signal may be adjusted to reflect the needs of a user's system. Typically, an interrupt request signal with a lower priority is adjusted to have the highest priority and is serviced first. An example of a data processor having an adjustable interrupt priority is the MC68HC11 of data processors sold by Motorola, Inc.
In known data processing systems, an interrupt request signal is not identified as having been adjusted. Often, it is desirable for the user to adjust the priority of a signal to a higher level without changing the interrupt request signal with the highest priority. Additionally, the user may need to determine whether or not an interrupt request signal has been adjusted to a higher level, or has simply been asserted in the general operation of the data processor. Existing data processing systems commonly use software routines which force every potential interrupt source to be investigated to determine if an adjustment in interrupt prioritization occurred. The time required to perform this function may significantly impact a system's overhead.